1. Field of the Invention
The present invention relates generally to apparatus for electrolytic surface treatment of a metal strip, for performing electrogalvanizing, electroleadplating, electrogilding, chemical conversion treatment, electrolytic pickling or degreasing and so forth. More specifically, the invention relates to a seal structure for an electrolytic cell which the electrolytic surface treatment apparatus is disposed, which establishes a liquid proof seal for preventing leakage of the electrolyte or electrolytic solution from the electrolytic cell. Further particularly, the invention relates to a seal structure for radial and counter flow type electrolytic treatment apparatus.
2. Description of the Background Art
Radial and counter flow type electrolytic treatment apparatus have been disclosed in the U.S. Pat. No. 4,500,400, issued on Feb. 19, 1985 to Akira Komoda et al. and in the U.S. Pat. No. 4,623,744, issued on Dec. 30, 1986 to Shinjiro Murakami et al, both have been assigned to the common assignee to the present invention. Such counter flow type electrolytic treatment apparatus, particularly electroplating apparatus have proved advantageous because of their capability of forming excellent plating layer.
On the other hand, in order to establish a counter flow of electrolyte or electrolytic solution in a direction opposite the feed direction of the metal strip, substantial pressure should be applied to the electrolyte or electrolytic solution. This pressure in the electrolyte tends to cause leakage of the electrolyte from the electrolytic cell. When leakage of electrolyte occurs, the electrolyte tends to come in contact with the backside surface of the metal strip which should not be treated thereby, resulting in partial corrosion or oxidation.
In order to seal the electrolytic cell, the Japanese Patent First (unexamined) Publication (Tokkai) Showa 60-215800, published on Oct. 29, 1985 and which has also been assigned to the common assignee to the present invention, discloses a seal structure for the electrolytic cell. The disclosed seal structure is successful in preventing leakage of the electrolyte or electrolytic solution. However, on the other hand, a seal segment has to be resiliently depressed onto the metal strip surface for establishing a satisfactorily liquid-tight seal, this tends to cause scratchs on the metal strip and/or the plated layer when dust or so forth adheres on the surface.
On the other hand, the Japanese Patent Second (examined) Publication (Tokko) Showa 49-2264 discloses electrolytic plating apparatus employing a rotary drum serving as supply electrode. In this device, an electrode formed on the rotary drum has to be sealed from the electrolyte so as not to be plated and to maintain electrically conductive contact with the metal strip. For this porpose, an electrode in a form of narrow circumferentially extending strip, is formed at about the axial center of the rotary drum. A rubber or other elastically deformable material seal layer is formed on both sides of the electrode for constantly contacting with the metal strip in a liquid-tight fashion for establishing plating protective seal for the electrode on the rotary drum. In this construction, when the metal strip is wrapped onto the rotary drum, the elastic seal layer tends to become deformed with the result that a step forms between the edge of the electrode. Scratches tend to be formed on the metal strip due to presence of the step between the elastic seal layer and the electrode.